title: Characterization of a novel missense mutation in the prodomain of GDF5, which underlies brachydactyly type C and mild Grebe type chondrodysplasia in a large Pakistani family.
abstract: All TGF-beta family members have a prodomain that is important for secretion. Lack of secretion of a TGF-beta family member GDF5 is known to underlie some skeletal abnormalities, such as brachydactyly type C that is characterized by a huge and unexplained phenotypic variability. To search for potential phenotypic modifiers regulating secretion of GDF5, we compared cells overexpressing wild type (Wt) GDF5 and GDF5 with a novel mutation in the prodomain identified in a large Pakistani family with Brachydactyly type C and mild Grebe type chondrodyslplasia (c527T>C; p.Leu176Pro). Initial in vitro expression studies revealed that the p.Leu176Pro mutant (Mut) GDF5 was not secreted outside the cells. We subsequently showed that GDF5 was capable of forming a complex with latent transforming growth factor binding proteins, LTBP1 and LTBP2. Furthermore, secretion of LTBP1 and LTBP2 was severely impaired in cells expressing the Mut-GDF5 compared to Wt-GDF5. Finally, we demonstrated that secretion of Wt-GDF5 was inhibited by the Mut-GDF5, but only when LTBP (LTBP1 or LTBP2) was co-expressed. Based on these findings, we suggest a novel model, where the dosage of secretory co-factors or stabilizing proteins like LTBP1 and LTBP2 in the microenvironment may affect the extent of GDF5 secretion and thereby function as modifiers in phenotypes caused by GDF5 mutations.
authors.affiliation: Laboratory of Genetic Skin Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata, 951-8510, Japan.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Farooq
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakai
authors.forename: Atsushi
authors.initials: A
authors.lastname: Fujimoto
authors.forename: Hiroki
authors.initials: H
authors.lastname: Fujikawa
authors.forename: Klaus Wilbrandt
authors.initials: KW
authors.lastname: Kjaer
authors.forename: Shahid Mahmood
authors.initials: SM
authors.lastname: Baig
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shimomura
mesh_terms: D000595:Amino Acid Sequence; D044466:Asian People / Q000235:genetics*; D059327:Brachydactyly / Q000235:genetics* / Q000503:physiopathology; D005838:Genotype; D055428:Growth Differentiation Factor 5 / Q000235:genetics* / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D053779:Latent TGF-beta Binding Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009139:Musculoskeletal Abnormalities / Q000235:genetics* / Q000378:metabolism; D020125:Mutation, Missense; D010009:Osteochondrodysplasias / Q000235:genetics* / Q000378:metabolism; D010154:Pakistan; D010375:Pedigree; D010641:Phenotype; D011487:Protein Conformation; D017422:Sequence Analysis, DNA
chemical_list: C525893:GDF5 protein, human; D055428:Growth Differentiation Factor 5; C509032:LTBP1 protein, human; C509035:LTBP2 protein, human; D053779:Latent TGF-beta Binding Proteins